Nondestructive reading of a ferroelectric capacitor
First Claim
1. A method of determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of:
- applying a first electric field of a first polarity to the ferroelectric capacitor to produce a first readout signal of a first polarity and a first magnitude;
applying a second electric field of a polarity different from that of the first electric field, across the ferroelectric capacitor to produce a second readout signal of a polarity different from that of the first readout signal;
combining electrical charges resulting from the first and second readout signals to produce a resultant signal representative of the polarization state stored in the ferroelectric capacitor; and
comparing the resultant signal with a reference voltage to produce an output digital state representative of the polarization state stored in the ferroelectric capacitor.
1 Assignment
0 Petitions
Accused Products
Abstract
A circuit and technique for accessing a ferroelectric memory to read polarization states without destruction thereof. A small-amplitude positive polarity pulse is applied to the ferroelectric capacitor, and the resultant positive charge read therefrom. Thereafter, a small-amplitude negative polarity pulse is applied to the ferroelectric capacitor, and the resultant negative charge read therefrom. Because of the nonlinear hysteresis characteristics of the ferroelectric capacitor, the positive and negative readout charges are of different amplitudes. Sense amplifier circuits produce a summation of the positive and negative readout signals, with a resulting summation polarity defining the polarization state initially stored in the ferroelectric capacitor.
82 Citations
37 Claims
-
1. A method of determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of:
-
applying a first electric field of a first polarity to the ferroelectric capacitor to produce a first readout signal of a first polarity and a first magnitude; applying a second electric field of a polarity different from that of the first electric field, across the ferroelectric capacitor to produce a second readout signal of a polarity different from that of the first readout signal; combining electrical charges resulting from the first and second readout signals to produce a resultant signal representative of the polarization state stored in the ferroelectric capacitor; and comparing the resultant signal with a reference voltage to produce an output digital state representative of the polarization state stored in the ferroelectric capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 33)
-
-
9. A method for determining a polarization sate of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising the steps of:
-
applying a word line signal to access the memory cell; applying a drive line voltage of a magnitude insufficient to change the polarization state to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second pulse having a polarity different from said first polarity pulse; generating a first capacitor readout signal on a bit line in response to the first polarity pulse; generating a second capacitor readout signal on the bit line in response to the second polarity pulse; and combining the first and second readout signals together to derive a resultant signal for use in determining the polarization state of the ferroelectric capacitor memory cell without destroying the polarization state. - View Dependent Claims (10, 11, 12, 13, 14)
-
-
15. A method for determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of:
-
applying an electric field across the ferroelectric capacitor of a first polarity and of such a magnitude that switching of the polarization state thereof does not occur, and producing a first readout signal; applying an electric field across the ferroelectric capacitor of a second polarity different from said first polarity and of such a magnitude that switching or a polarization state thereof does not occur, and producing a second readout signal; and determining the polarization state of the ferroelectric capacitor by combining the first readout signal having a defined magnitude and polarity with the second readout signal having a different polarity to obtain a resultant polarity, and assigning the polarization state based upon the resultant polarity. - View Dependent Claims (16, 17, 18, 19)
-
-
20. A nonvolatile ferroelectric memory, comprising:
-
a drive line; a bit line; at least one memory cell having a ferroelectric capacitor in series with a transistor switch, said cell being connected between said drive line and said bit line; a word line connected to said memory cell for controlling the transistor switch; a sense amplifier circuit connected to said bit line, said sense amplifier circuit including, a first storage capacitor for storing a first readout signal from said ferroelectric capacitor; a second storage capacitor for storing a second readout signal from said ferroelectric capacitor; isolation means for isolating said first and second storage capacitors from each other; and combining means for combining the charge stored in said first and second storage capacitors; and amplifier means for amplifying a signal representative of the combined charge to provide a digital output signal representative of a polarization state of the ferroelectric capacitor. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
-
-
34. Apparatus for determining a polarization state of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising:
-
means for applying a word line signal to access the cell; means for applying a drive line voltage to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second different polarity pulse; means for generating a first ferroelectric capacitor readout signal on a bit line in response to the first polarity pulse; means for generating a second ferroelectric capacitor readout signal on the bit line in response to the second polarity pulse; and means for combining together electrical charges representative of the first and second readout signals to determine a resultant first or second polarity that corresponds to the polarization state of the ferroelectric capacitor. - View Dependent Claims (35, 36, 37)
-
Specification